Multilayer polymeric films are commonly used for packaging products such as snack foods, including candies, potato chips, cookies, ice cream bars and dairy products. The versatility and compositional variation of polymer films facilitate usefulness in a variety of packaging applications. A wide array of film compositions are available today due to custom tailoring a multitude of variables related to polymer composition, additives, and method of preparation of the film to suit a particular product application and service environment. Seemingly small changes in composition or properties often determine whether or not a film will perform suitably. For example, although polymer films have many desirable properties, untreated or uncoated films may possess certain inherent disadvantages, such as relatively poor water wetability, poor printability, poor barrier properties and/or blocking with adjacent film layers.
Frequently, a primary concern in designing multiple-layer films for packaging is to ensure that the film can be processed, prepared and utilized on high speed converting and form-fill-and-seal (“FFS”) machinery. Vertical FFS packaging apparatus operate by unwinding continuous film from bulk rolls, pulling the film over a forming collar, followed by forming pouches or bags by sealing lower and side portions of the package, filling the package, and finally sealing the upper portion to close the package. Horizontal FFS packaging apparatus operate by unwinding continuous film from bulk, aligning the film along a horizontal track, positioning the product or container, such as an item or box, on the film in a determined position and orientation, followed by forming and bending the film around the product or container, either snuggly or loosely, to form a package, and thereafter sealing the package closed.
Therefore, in many packaging operations, the film must have sufficient flexibility and machinability to undergo mechanical folding from a roll-fed or flat orientation to a folded condition and be subjected to a sealing function which is part of high-speed packaging apparatus. The higher the packaging speed, the more difficult this operation becomes. In addition to aesthetic and optical qualities, the ability of the film to perform reliably on high speed equipment, including unrolling, processing, folding and sealing equipment, are typically primary objectives in film composition design. Line speed is dictated by a number of factors, including friction with machinery, blocking tendencies, sealability, and packaged product interaction with the film. For many such packaging operations, the product-film interaction factor is not a big consideration. However, for some applications, such as foods, powders, grease-bearing products, and moist or wet products, this factor may become of quite significant importance with respect to the interaction over an extended period of time. An additional consideration for the product-film interaction factor is the interaction precisely during packaging operations, as this factor may significantly control the ability to increase packaging operation speed.
The performance of a film embodiment, during packaging operations, may vary with changes in environmental conditions and can adversely impact properties on one or both sides of a film. For example, in a dairy environment where frozen ice cream novelties and frozen water-based pops may be packaged, temperature and humidity conditions may vary widely and inconsistently at various regions within the facility, and within the vicinity of packaging operations, where the packaging equipment and processes are located. For example, the packaging film may be utilized in relatively dry conditions for a period of time and then under more humid and even wet conditions at another time, when the packaging equipment and/or adjacent packaging equipment is washed with water, which may occur several times per day. Also, the composition of the products on a line may vary widely, such as from sugar-based to sugar-free variety of a product.
In a humid or wet environment, undesirable friction characteristics may adversely affect the performance of either or both sides of the film. Friction between packaging equipment surfaces and the film, and/or between the product and the film may cause packaging imperfections and impede high-speed processing. For example, frozen pops or ice cream bars that are made from a syrup, cream or sugar-based solution may readily adhere and “tack-up” as the product engages the product side of the film, remaining in the proper position and orientation for the packaging process, while a sugar-free version of the product may slide or reorient on the film during packaging operations, resulting in either operational problems and slowing down the packaging line to accommodate the product variations. A misaligned product may create increased product waste, film waste, machine damage and down-time, due to the product getting caught or chopped in the seals during the packaging process.
On the opposite side of the film, the machine side, the film must be able to slide over a variety of stationary, rotating, metal, nonmetal, heated, and/or refrigerated surfaces, while maintaining a stable coefficient of friction and good slip characteristics relative to all of the surfaces. As relative humidity increases and condensation forms on equipment, the moisture may adhere to the film creating an excessive staccato movement of the film as the film repeatedly sticks and then releases from the wet machine surfaces. This staccato movement frequently results in inconsistent package length, film jams, tears, and exaggerated product misalignment problems on the opposing, product side of the film.
There exists in the art, the need for a sealable film with improved processability, machinability, and reliability over a range of temperature, relative humidity and dampness conditions, ranging from relatively dry to a substantially wet environment, without adversely impacting other desirable film parameters, such as film sealability, moisture barrier properties, interaction with the packaged product, and optical and appearance properties.